A special alpine unit of the French gendarmerie said yesterday that there was no immediate explanation for the fall of the two young British climbers.

“These two climbers came unstuck for an unknown reason and fell for nearly 600 metres while they were climbing in the the Couloir Gerbasutti on the eastern face of Mont Blanc,” a spokesman for the Gendarmerie de Haute Montagne said yesterday.

Another officer said that there had been no reports of avalanches at that time in that part of the Mont Blanc massif. “There might have been a smaller, local, ice fall, as temperatures fluctuate, but it is too early to say,” the officer said.

"It appears that these climbers were experienced and well-equipped. At present, the accident is difficult to explain but often, if there are no witnesses, it is that way."

Mr Gauntlett climbed Everest when he was just 19. His parents have flown to France. Speaking from the family home in Petworth, West Sussex, on Saturday night, his mother Nicola said: “We are all just devastated. He's far too young to die.

“We had spoken about this happening only recently. We can only take consolation that he died doing something that he loved.”\[Michael Hall\]James Hooper, 21, with whom Mr Gauntlett climbed Everest in 2006, when they were just 19, said he had been with the pair shortly before their deaths. But he said as the two most experienced mountaineers, he and Mr Gauntlett had split up with their two less experienced friends.

"Rob and James went off to do a route and my friend and I looked at a route, but didn't like the look of the weather so we decided not to," he said.

"Then the weather suddenly cleared up but by that time it was too late for us to start our route and we decided to come down. Then Rob and James stayed up there and they were trying to do a big route yesterday morning and fell."

He paid tribute to Mr Gauntlett with whom he had climbed for years.

"Rob and I have been best friends since we were 15 and so we obviously knew each other really well and have been on lots of expeditions together", he said.

"He was practically a brother to me. I'm obviously devastated but I'm just trying to remember the fact that he was a wonderful person and he inspired me and others in so many different ways.

"Rob was so ambitious and driven to get the most of life and have the best experiences. He really pushed himself as hard as he could. It was only because he was such a motivated and driven person that the accident happened, but those were the qualities that made him so incredible. I certainly wouldn't have been able to achieve any of it without Rob. We worked as a team and without him we wouldn't have been able to do it."

He also saluted Mr Atkinson, a Durham University student from Sussex, as a "top guy" who was highly motivated about outdoor pursuits.

\[Michael Hall\]"He loved climbing and he loved cycling and he has been a great friend of ours for many years.

"This time in Chamonix was the first time that the group of all four of us best friends have been able to get away and have a big holiday together."

A tribute page has been set up on the social networking website, Facebook, called RIP Rob Gauntlett. One said: "His loss is as tragic as it is untimely. Maybe it's some consolation that he managed to pack more into his 21 years than most of us would ever in 70."

Mr Gauntlett and Mr Hooper hatched a plan to climb Everest during their GCSEs, which they succeeded in doing three years later.

Speaking from the summit in May 2006, Mr Gauntlett said: "James and I are really keen on getting the message out to young people to follow your dreams.

"This has been our dream for three years."\[Michael Hall\]Mr Gauntlett, who was also a keen cyclist, continued to take on extreme challenges and in March 2007, he and Mr Hooper set off on a journey from the North Geomagnetic Pole to the South Magnetic Pole using entirely human and natural power.

Over the next 13 months, the adventurers travelled 26,000 miles using methods including skis, dog sleds, cycling and sailing to cross land, sea and ice.

While skiing between Canada and Greenland, Mr Gauntlett fell through the melting sea ice and was left unconscious for three hours as Mr Hooper phoned for help to organise their evacuation to safety.

Mr Gauntlett was a motivational speaker with Mr Hooper, with their website stating: "They are keen not only to emphasise the importance of protecting our environment through education and lifestyle choices, but also to ignite a flame in everyone they meet which pushes them to utilise their talents and achieve their ambitions."

Anna Gregory, secretary of the London and South East branch of the British Mountaineering Council, said that although she did not know Mr Gauntlett, he was an inspiration to climbers.

She said: "He had plans and wanted to gain records - we were looking forward to his next achievement."